There are many different types of rotary surface finishing discs on the market, each designed for a particular aspect of a finishing process. Generally speaking, these finishing discs include abrasive particles which are attached to a backing, such as with adhesive. Typically, the abrasive particles are located on the side of the disc that is intended to come into contact with a work surface when the disc is mounted to a surface finishing tool.
Surface finishing tools generally include a motor which rotates the finishing disc. The abrasive particles are positioned on the disc to contact the work surface, scraping off the top coating or layer of the work surface. A common type of disc used with these sanders includes a fiber substrate onto which sharp, abrasive particles are securely bonded with a phenolic resin coating. The cured resin coating locks the sharp abrasive particles onto a fiber substrate.
The design of a rotary abrasive disc requires balancing the operational life of the disc against the "aggressiveness" of the abrasive. Aggressiveness relates to how much surface material is removed by the disc. In order to provide a high degree of aggressiveness, it is desirable to have relatively large abrasive particles on a rigid substrate, such as a resin fiber. However, an aggressive abrasive surface has drawbacks which limit its effectiveness. For example, during use, the larger abrasive particles, which are the first particles to contact the work surface, begin to wear and become dull, leading to the formation of flat spots on the disc. The flattened particles, too dull to continue to cut, "ride" on the work surface and prevent the smaller, still sharp, abrasive particles from contacting the work surface. This is commonly referred to as "glazing". Testing has shown that the flattening or glazing of as little as 10% of the disc surface may be sufficient to render the entire disc unusable. As a result, the disc must be replaced after a relatively short period of time. While it is possible for the operator to increase the amount of pressure exerted on the disc to force the smaller abrasive particles into contact with the work surface and, thereby increase the amount of cutting provided by the disc, the extra exertion will result in increased operator fatigue. Also, the build-up of non-cutting grit on the disk results in the development of excessive heat.
Another drawback to the use of resin fiber discs is that the material removed from the workpiece tends to become lodged between the large abrasive particles, "loading" the abrasive and preventing the abrasive particles from effectively cutting the surface. Consequently, during a typical surface finishing operation, an operator will be required to replace the abrasive disc several times due to wear. While changing one disc may only take several minutes to accomplish, the cumulative down-time involved in changing several discs can be quite significant.
Another problem with conventional surface finishing discs is that they are not designed to adequately finish interior corners on a work piece. The tight corner formed by converging surfaces of a work piece prevents a finishing disc from easily and efficiently sanding the interior corner. Currently, interior corners need to finished by inserting a one sided disc into the notch to sand one side of the surface. The tool is then reversed to permit the disc to sand the other side of the notch. This is a very time consuming and tedious process, and does not provide consistent surface finishing.
Furthermore, many conventional surface finishing discs are inefficient since only a portion of the finishing disc is in proper contact with the work surface. This portion wears considerably faster than the other portions of the disk that are not contacting or only minimally contacting the work surfaces. When a portion of the conventional disc has worn out, the entire disc must be replaced.
A new development in the field of sanding devices is the rotary flap disc which includes a series of rectangular abrasive flaps mounted around the circumference of a backing plate. The flaps utilized in these discs have abrasive particles adhesively bonded to a substrate, such as cotton or polyester cloth, by means of a phenolic resin. The unique feature of flap discs is that the rectangular abrasive flaps overlap one another in a stacked or shingled arrangement. As the exposed edges of the abrasive flaps begin to wear, the dull abrasive particles begin to break away from the substrate and are removed from the workpiece with the chips. The exposed fibers of the substrate quickly wear and break away, exposing the new abrasive particles on the underlying flap. Hence, the operator can continue to sand for a longer period of time before having to stop and change discs. As a result, the down-time in the sanding process is significantly reduced.
U.S. Pat. No. 5,752,876 discloses one very successful rotary flap disc design.
U.S. Pat. No. 5,752,876 is incorporated herein by reference in its entirety.
Although rotary flap discs are available on the market, the concept of a flap-type disc has not been applied to surface finishing discs for finishing odd shaped surfaces and interior corners, such as a V-shaped groove.
A need exists for an improved finishing disc which is designed to provide efficient and even finishing of an interior corner, such as a V-shaped groove, in a work piece.